To emphasize Daniel's great comments, slope (up or down) is the largest factor concerning road placements, especially if there is wheeled traffic on it (human and horse trails differ...) Early roads will fo 10x the distance to avoid going up or down steep slopes. Where there is no choice, switchbacks are typically employed.

A bunch of random and possibly incorrect thoughts:

Straight (and possibly cobbled/paved) overland roads tend to be created when there is a large empire, and are primarily created to move armies.

In a medieval/fantasy setting there should also be a large emphasis on water transport, so many roads will tend to converge on harbours, etc.

Bridges are expensive, so most river crossings should be with barges/ferries or fords and in either case will be a flat areas where the water is shallow and slower. Roads may parallel a waterway to get to such a crossing.

Trails and roads often follow rivers.

Trunk/branch roads tend not to exist, with many roads connecting point to point between destinations. For example, 4 towns forming a square will most likely have a road/trail between each town, terrain permitting, to minimize the distance to travel. (See previous comment on straight roads for when "kings highway" type roads show up).

Roads get built on trails, which are built on paths, etc, so they evolve more than are planned.

Often towns end up at crossroads, mainly to service multi-day travel. (i.e. town is there because of the road, rather than the road is there because of the town).

-Rob A>